Depends entirely on the item; furniture, whitegoods, cars, easily damaged items, etc are quite understandable. 

With smaller but heavy items, a lot of sellers don't think people will pay $20--$30 postage, so don't list postage as an option. You won't know unless you ask - and I'd much rather a buyer ask rather than just blindly bid.

I asked the very same question of a seller late last week - he replied that he'd post at my expense, I bid on and won the item, and it arrived on Sunday. Result: I got a sought-after item, and the seller got $120 more for it than he would have if I hadn't bid and the under-bidder had won it.

Mind you, I've also had sellers refuse to post magazines, insisting on pick-up. Seriously...